Re: Old overflow expansion tank

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Posted by Harold Kestenholz - Hydronic Network on November 13, 2001 at 08:46:31:

In Reply to: even more questions? posted by jennifer on November 12, 2001 at 21:27:28:

You are describing the original concept of expansion tank that was used before there was city water available and after. Originally many systems were filled by hand into that tank at the top. The system was full when the tank was full. The overflow pipe to a sink, tub, outdoors or basement tub prevented water damage when the water expanded as it was heated. Yours flooded because you have city water to push much larger amounts of water than the original installers thought would be available.

The system seems to still be an unsealed atmospheric pressure system that uses the height of the tank to provide enough pressure to push air out of radiator vents when opened while the tank provides a reservoir for a little extra water to allow for evaporation and expansion room. The pressure on the boiler gauge would stay steady at all times; it is necessary for the purposes of the ASME to indicate overpressure. The 25 psig reading was a sure indication that the tank was overfilling.

Now that the tank is full, mark the gauge with a magic marker at the point the indicator is now, probably 14, 16 psig or so (wherever the needle now points.) To know when the tank is near full when filling, look at the gauge; the needle should not rise above that mark. Extra water will fall back down the overflow pipe to indicate you should close the water.

The advice to pack the valve stem with graphite was good; but more needs to be done. Valve packing can be done by using a hooked pick (like the old button hooks or dentists picks) to remove the old packing. Cotton, oak, or soft hemp cord smeared with graphite was cut into circles to be stacked (alternating the slanted cuts atop one another) to make a packing that would swell when wet under the packing nut. If it is just the stem packing that is leaking, this can save the valve.

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